Twelve-year-old Owen Baker (Liam Aiken) has been working hard as a dog-walker all summer, and his hard work has finally paid off - he gets to adopt a dog of his own! But Owen gets more than puppy love when he discovers his new dog, Hubble (voiced by Matthew Broderick), is actually an interplanetary scout from the Dog Star, Sirius.

Thousands of years ago, dogs from Sirius came to colonize and dominate Earth. But rumors have spread across the galaxy that these Earth dogs have strayed from their original mission, and Hubble has been sent to investigate. Now Owen must help Hubble train a group of undisciplined neighborhood dogs to shape up for a visit from their leader, the powerful Greater Dane - and the fate of all Earth dogs hangs in the balance.